The present invention relates to solid-state area imaging apparatus and more particularly to a solid-state area imaging apparatus suitable for photographing still pictures.
The solid-state area imaging devices heretofore known in the art include for example FT-CCD (frame transfer-charge coupled device) and IL-CCD (interline transfer-charge coupled device).
With the FT-CCD, its photosensitive means also serves as vertical transfer means and its stored charges are transferred vertically by the vertical transfer means. To effect the vertical transfer, only alternate lines, i.e. either the odd horizontal scanning lines or the even horizontal scanning lines, can receive the light at a given time instant. Here, each of the odd and even horizontal lines indicates a straight line formed by connecting light signal charge storage positions and thus it is an imaginary line corresponding to the horizontal scanning line in an image pick up tube. Thus, in accordance with this invention the term horizontal scanning line means such a line.
Where this type of CCD is used as a video camera solid-state area imaging device, the use of the interlaced scanning determines a vertical resolution which is dependent on the number of vertical electrodes or the number of picture elements. However, where a still picture is reproduced on a television receiver by a still camera, there is the restriction of the same exposure time at the same time with the result that only one field comprised of either the odd horizontal scanning lines or the even horizontal scanning lines can be used as the light signal charges and consequently only the alternate lines can receive the light. Thus, the resulting resolution is one half that obtained by using all the scanning lines of the television picture. Even if the video signal of either one of the fields is reproduced by applying a pseudo interlaced scanning to the odd or even field, the resolution of the resulting still picture cannot attain the level obtained by using all the scanning lines.
On the other hand, the IL-CCD includes separate photosensitive means and vertical transfer means and thus the picture information can be applied simultaneously to all the photosensitive elements or all the picture elements. In this case, however, the light signal charges of the photosensitive elements are read out field by field by dividing the still picture into the odd fields by the odd horizontal scanning and the even fields by the even horizontal scanning. Thus, while there will be no problem if a mechanical shutter is used, if no mechanical shutter is used, during the time that the light signal charges of one of the two fields are transferred vertically (1/60 sec.), the photosensitive elements of the other field are exposed to the light with the resulting difference in picture information between the two fields. Thus, if the picture information is recorded and reproduced as such, a reproduced picture of good quality cannot be obtained and therefore only the video signal of one of the two fields can be used, giving rise to a problem from the standpoint of vertical resolution as in the case of FT-CCD mentioned previously.